1. Field of the Invention
The present invention relates to a braking apparatus of a vehicle equipped with a regenerative brake device and a friction brake device, and more particularly, to techniques of controlling braking force when automatic braking is executed by a collision avoidance device.
2. Description of the Related Art
A vehicle equipped with an electric motor for running the vehicle, such as an electric vehicle or hybrid vehicle, is conventionally provided with a regenerative brake device that uses the electric motor as an electricity generator when the vehicle is decelerating or running down a slope, to convert deceleration energy into electric energy to charge a battery mounted on the vehicle.
Such a vehicle equipped with a regenerative brake device is provided further with a friction brake device that brakes the vehicle by frictional force in response to operation of a brake pedal, like a hydraulic brake device.
Meanwhile, in recent years, more and more vehicles have come to be equipped with a collision avoidance device that detects an obstacle when the vehicle is running, and automatically brakes the vehicle if there is a risk of the vehicle colliding with an obstacle.
Further, a braking force control device for a vehicle equipped with a collision avoidance device, a regenerative brake device and a friction brake device has been proposed, in which the braking force generated by the friction brake device and that generated by the regenerative brake device are controlled when the automatic braking is performed for collision avoidance. In the device disclosed in Japanese Patent No. 3888383 by way of example, when the demanded braking force calculated based on the distance to an obstacle is smaller than a predetermined value, the regenerative braking alone is activated, and when the demanded braking force is greater than the predetermined value, both the regenerative braking and the friction braking are activated to secure sufficient braking force.
In the vehicle equipped with a collision avoidance device, a regenerative brake device and a friction brake device like the one disclosed in the above patent publication, if the battery becomes fully charged, for example, while both the regenerative braking and the friction braking are executed during the automatic braking for collision avoidance, electricity cannot be supplied to the battery any longer, with the result that the regenerative braking terminates. Thus, because of the termination of the regenerative braking, the braking force and, as a consequence, the rate of deceleration of the vehicle fluctuate during the automatic braking, causing a feeling of strangeness and possibly increasing variation in the braking distance.